Date:	Sun, 8 Mar 1998 14:46:29 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	DJ Delorie <dj AT delorie DOT com>
cc:	djgpp-workers AT delorie DOT com
Subject:	Making `open' *really* fail under O_EXCL
Message-ID:	<Pine.SUN.3.91.980308144408.22686j-100000@is>
MIME-Version:	1.0

There is a small window of opportunity for `open' to not fail under 
O_EXCL, if some other process creates while `open' runs.  Here's a patch 
to close that window.

*** src/libc/posix/fcntl/open.c~0	Sun Nov 16 19:05:00 1997
--- src/libc/posix/fcntl/open.c	Fri Mar  6 19:12:28 1998
*************** int
*** 17,25 ****
  open(const char* filename, int oflag, ...)
  {
    int fd, dmode, bintext;
  
    /* Check this up front, to reduce cost and minimize effect */
!   if ((oflag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL))
      if (__file_exists(filename))
      {
        /* file exists and we didn't want it to */
--- 17,26 ----
  open(const char* filename, int oflag, ...)
  {
    int fd, dmode, bintext;
+   int should_create = (oflag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL);
  
    /* Check this up front, to reduce cost and minimize effect */
!   if (should_create)
      if (__file_exists(filename))
      {
        /* file exists and we didn't want it to */
*************** open(const char* filename, int oflag, ..
*** 39,60 ****
  
    dmode = (*((&oflag)+1) & S_IWUSR) ? 0 : 1;
  
!   fd = _open(filename, oflag);
! 
!   /* Under multi-taskers, such as Windows, our file might be open
!      by some other program with DENY-NONE sharing bit, which fails
!      the `_open' call above.  Try again with DENY-NONE bit set,
!      unless some sharing bits were already set in the initial call.  */
!   if (fd == -1
!       && ((oflag & (SH_DENYNO | SH_DENYRW | SH_DENYRD | SH_DENYWR)) == 0))
!     fd = _open(filename, oflag | SH_DENYNO);
!   if (fd == -1 && oflag & O_CREAT)
!     fd = _creat(filename, dmode);
  
    if (fd == -1)
      return fd;	/* errno already set by _open or _creat */
  
!   if (oflag & O_TRUNC)
      if (_write(fd, 0, 0) < 0)
        return -1;
  
--- 40,66 ----
  
    dmode = (*((&oflag)+1) & S_IWUSR) ? 0 : 1;
  
!   if (should_create)
!     fd = _creatnew(filename, dmode, oflag & 0xff);
!   else
!   {
!     fd = _open(filename, oflag);
! 
!     /* Under multi-taskers, such as Windows, our file might be open
!        by some other program with DENY-NONE sharing bit, which fails
!        the `_open' call above.  Try again with DENY-NONE bit set,
!        unless some sharing bits were already set in the initial call.  */
!     if (fd == -1
! 	&& ((oflag & (SH_DENYNO | SH_DENYRW | SH_DENYRD | SH_DENYWR)) == 0))
!       fd = _open(filename, oflag | SH_DENYNO);
!     if (fd == -1 && oflag & O_CREAT)
!       fd = _creat(filename, dmode);
!   }
  
    if (fd == -1)
      return fd;	/* errno already set by _open or _creat */
  
!   if ((oflag & O_TRUNC) && !should_create)
      if (_write(fd, 0, 0) < 0)
        return -1;
  
*** src/docs/kb/wc202.t~4	Fri Mar  6 19:31:56 1998
--- src/docs/kb/wc202.txi	Fri Mar  6 19:37:42 1998
***************
*** 340,342 ****
--- 340,348 ----
  that no other process can neither read from nor write to it.  In case of
  a failure, @code{tmpfile} does not leak memory anymore.
  @findex tmpfile
+ 
+ Previously, there was a small probability that a call to @code{open}
+ with the @code{O_CREAT} and @code{O_EXCL} bits set would succeed even
+ though the named file already existed (created by another process).
+ This window is now closed.
+ @findex open

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